We have just passed the winter solstice here at Londolozi which means, on the 21 June, we experienced our shortest day and our longest night as the southern hemisphere reaches its furthest point away from the sun on its 365 day orbit. What this means for us on safari is that we are out on game drives a bit later in the morning and a bit earlier in the afternoon. The timing of our sundowner stop is essential, ensuring that everyone is comfortable, drink and snacks within reach, and with ample time to see one of Africa’s sensational sunsets. The management of our shortened hours got me thinking about light and the role it has in our lives and more specifically our ecosystem.
What is light?
So what is light? Light is energy. All of the natural light we have on Earth is produced by the nuclear fusion of hydrogen nuclei combining together to form helium. During this process a very small amount (less than 1%) of mass is released as energy which makes its way to the surface of the sun before beaming out into space, travelling at 300 000 km/sec and reaching the earth in 8 minutes. All this sounds very scientific and difficult to comprehend so to put this in perspective it is the equivalent of flying around the equator in less than a quarter of a second!
What is the Electromagnetic Spectrum?
The light we see as white light is in fact made up of a whole spectrum of wavelengths called the Electromagnetic Spectrum (EMS), of which our eyes have only evolved to be able to see a narrow range. Each range is defined by different wavelengths and hence within the visible range (picture the colours of the rainbow) the shorter the wavelength the more blue the colour versus the red colour of the longer wavelengths.
The most evident example of this in our day to day safaris is the difference in the colour of the sky during the day versus at sunrise or sunset. As the sunlight is passing through space and hits our atmosphere it gets scattered in all directions by the gas molecules and particles that make up our atmosphere. Blue light is scattered more than the other colours as it travels in shorter, smaller waves. This is why we have a blue sky.
At sunrise and sunset, when the sun is just above the horizon, the light needs to travel through more of our atmosphere to reach our eyes and the shorter wavelengths are scattered so much that they don’t reach our eyes and only the reds, oranges and yellows reach our eyes creating the beautiful mosaic of colours of a bushveld sunrise or sunset.
How Do Plants Use Light?
Now that we know what light is and what it is made up of. What is one of its most important roles in life as we know it? Photosynthesis. Plants form the basis of all life on Earth. They are the producers at the base of the trophic pyramid and without them, none of our herbivores would be able to eat and we’d have none of the incredible predators that we all love to get a glimpse of when on safari.
Plants need three things to photosynthesize:
- Carbon dioxide
Photosynthesis allows the plant to create carbohydrates that give all the cells in the plant the energy to perform their tasks; be that sucking up water by the roots, creating its protective bark around the trunk of the tree, or any of the other myriad functions a plant performs to grow. The byproduct of photosynthesis, oxygen, is equally as important as the food that plants provide to all the herbivores on Earth. Without this the Earth as we know it would be a very different place.
How Do Birds Fit In?
Birds are another fascinating example of how animals have evolved to use natural light for several different uses. In recent years, researchers have found that birds have the ability to see light with shorter wavelengths outside of the visible spectrum; these are included in the ultraviolet (UV) spectrum. What this means is that the vibrant colours of bird plumage could in fact be even more colourful to another bird than to the human eye.
Perhaps the LBJ’s (Little Brown Jobs) that we think are all so similar in plumage are in fact more different than we think – but that’s a whole different topic on its own.
Not only can this ability to see in the UV spectrum benefit birds from a breeding perspective but birds have also harnessed this ability to better aid them in meeting their daily food demands. Hawks have been found to follow rodents whose urine leaves trails in the UV spectrum. Some plants advertise their seeds to seed-dispersing birds with UV reflectance and there is research into the ability of insect-eating birds to be using UV traces given off by insects to decipher the correct insects to go for while hawking through the skies.
What effect does light have on animals?
Animals are also affected by light. We have just come to the end of the impala rut; their breeding season where the males spend the majority of their day rounding up females to ensure they have the opportunity to mate and pass on their genes to the next generation. During this rut, the males experience a heightened level of testosterone which is triggered by the shortening of days. The pituitary gland, which is a small pea-sized gland in the brain, controls the hormones released to the body. The fact that this rut is triggered during this period where the days are shortened means that the females will all give birth within a 6-week window later in the year. This strategy of essentially “flooding the market” with young lambs gives the species the best possible chance of having a high percentage of their lambs making it to adulthood.
These are but a few of the different functions which light plays in our ecosystem but what I love about the topic of light is the interconnectedness of all the different aspects we come across on a daily basis. As scientists globally explore better ways for us to harness the energy of the sun, perhaps the examples we see in our ecosystem will shed more light on the matter.